Aluminum/lithium alloys have been proposed for many years, and several Al/Li alloys are produced commercially. Lithium, in appropriately formulated alloys, tends to increase alloy strength while providing for a lower density alloy at the same time. However, lithium is a very reactive metal, and smelting opera- tions are problematic. In some alloys and furnaces, the alloys are known to react with the refractory furnace lining, while other alloys are explosively oxidizable. Those factors increase the cost of the alloys considerable. A thorough discussion of aluminum/lithium alloys and some of the problems associated with their preparation and use may be found in Pickens et al, U.S. Pat. No. 5,211,910.
For these reasons, Al/Li alloys are generally reserved for applications where strength/weight ratios and other requirements outweigh cost disadvantages. However, even for many such applications, problems associated with such alloys such as weldability, work hardening, and the like render these alloys unsuitable. One example is the manufacture of fuel tanks for the aerospace industry. Several Russian alloys, i.e. 1421 and 1460, employ specific alloy compositions which encourage weldability. These alloys, like those discussed in U.S. Pat. No. 5,211,910, employ a modest amount of copper along with lithium. However, the Russian alloys also add a small amount of scandium. While these alloys exhibit vastly improved weldability, their physical properties, particularly short transverse properties, are severely deficient.
It would be desirable to provide sheet materials which offer high strength characteristics, uniform properties, i.e. which are substantially isotropic, and yet which are weldable.